An organic electroluminescent element (hereinafter, referred to as “organic EL element”) utilizing electroluminescence (hereinafter, referred to as “EL”) of an organic material is a thin-film type completely-solid state element capable of emitting light at a low voltage of several volts to several ten volts, and has many excellent features such as high luminance, high light-emission efficiency, small thickness and light weight. Accordingly, in recent years, the element has attracted attention, as backlights for various kinds of displays, display boards such as a signboard and an emergency lamp, and surface emitting bodies such as illumination light sources.
Such an organic electroluminescent element has a configuration obtained by holding a light-emitting layer formed of an organic material between two electrodes, the emitted light generated in the light-emitting layer is extracted to the outside through the electrode. Therefore, at least one of the two electrodes is constituted as a transparent conductor.
As the transparent conductor, there have been examined a material of an oxide semiconductor type such as indium tin oxide (Indium Tin Oxide: ITO), and a material aiming at lowering electric resistance by laminating ITO and silver (e.g. refer to the following Patent Literatures 1, 2). However, ITO has a high material cost because of using a rare metal indium, and is required to be subjected to annealing treatment at about 300° C. after the formation in order to lower its electric resistance. Accordingly, there has been proposed a configuration in which an electrical conductivity is ensured even at a film thickness smaller than that of silver alone by blending aluminum with silver (e.g. refer to the following Patent Literature 3).